To provide an electron beam irradiation device capable of avoiding a problem of convergence of an electron beam at the maximum scanning points, and constantly obtaining an irradiated region of uniform energy density, an electron beam irradiation device comprising an electron beam source 12, an accelerating tube 13 for accelerating electrons emitted from said electron beam source, a focusing electromagnet 16 for applying a magnetic field to a high energy electron beam, which is formed by the accelerating tube, for controlling the beam diameter of the electron beam, and an electromagnet 17 for deflecting and scanning the beam-diameter-controlled electron beam by applying a magnetic field to the electron beam, wherein an electric current component I.sub.F which is synchronized with an electric current I.sub.S of the scanning electromagnet 17 is superimposed on an electric current IF of the focusing electromagnet 16, thereby controlling the electric current I.sub.F of the focusing electromagnet in a manner that said beam diameter becomes maximum at the maximum scanning points.